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An aircraft is a machine that can fly with the help of buoyancy, or wings, blades or in some cases, an engine pointing downwards or at an angle, pushing it off the ground. Aircraft can generally be either powered by an engine or without an engine. In all these cases, an aircraft has to overcome the gravity with the help of two forces called thrust and lift.
Frequently Asked Questions
How does a buoyant aircraft work?
Hotter air rises in cooler air. A hot air balloon is a good example for a buoyant aircraft that uses the upthrust or buoyancy to fly. Hot air rises due to the fact that it is less dense than the cooler air surrounding it. This difference in density between the hot air inside the balloon and the atmospheric air forces the balloon to rise up in the atmosphere, generating an upward lift, usually called as an upthrust. As the hot air inside is lighter than that of the surrounding air, it is generally called as a lighter than air aircraft.
How does an aircraft with wings work?
An aircraft with wings work by moving through the air, at an angle, with or without the help of an engine. The wings are shaped in a way that when they move through the air at a certain angle called, the angle of attack, they can push the air downwards as it moves forward. The shape of a wing's cross-section is called as an airfoil. This could be practically understood by placing one's palm outside a moving car at an angle, like an aircraft's wing. In actual wings, due to its airfoil, at a certain angle of attack, the flow field creates a high-velocity and a low-pressure area at the upper surface of the wing and a low-velocity and a high-pressure area at the lower surface. Following the Bernoulli's principle, the overall pressure difference creates lift, which is NOT the key factor for an aircraft to fly. Although there is a little amount of lift produced due to the Bernoulli's principle, the actual lift is produced by the Newtonian force. This could be explained by Newton's third law. When the air hits the wing, the shape of the airfoil deflects the air downwards, thereby exerting an equal and opposite force. Most aircraft as we see around are usually powered by an engine to provide the thrust required to move through the air so that the wing can produce lift. However, there are aircraft like gliders and kites that are not powered.
Are there any aircraft that is powered by rockets?
Yes, there were. Mostly, experimental aircraft that either used rockets to assist them in take-off and landing or used them along with air-breathing engines to achieve higher speeds. A notable rocket-powered aircraft is the North American X-15, that used only a liquid propellant rocket engine to attain hypersonic speeds.